EP3002450B1

EP3002450B1 - Engine system and straddled vehicle

Info

Publication number: EP3002450B1
Application number: EP15185919.6A
Authority: EP
Inventors: Seigo Takahashi; Takahiro Masuda; Yuki Yamaguchi
Original assignee: Yamaha Motor Co Ltd
Current assignee: Yamaha Motor Co Ltd
Priority date: 2014-10-02
Filing date: 2015-09-18
Publication date: 2018-02-28
Anticipated expiration: 2035-09-18
Also published as: TWI596274B; JP2016070259A; EP3002450A1; TW201625844A

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an engine system and a straddled vehicle including the engine system.

Description of Related Art

In a straddled vehicle such as a motorcycle, a large torque is necessary in order for a crank angle to exceed an angle corresponding to a first compression top dead center during a start-up operation of an engine. Therefore, there is a technique for rotating a crankshaft in a reverse direction in order to increase startability of the engine.
In an engine system described in JP 2014-77405 A , during start-up of an engine, a fuel-air mixture is introduced into a combustion chamber while a crankshaft is rotated in a reverse direction. With the fuel-air mixture being compressed in the combustion chamber, an ignition operation by an ignition device is performed. Thus, the fuel-air mixture is combusted, so that rotation of the crankshaft is driven in a forward direction by energy of the combustion.

BRIEF SUMMARY OF THE INVENTION

The inventors of the present invention have discovered by performing a variety of experiments and analysis that variations are generated in pressure in the combustion chamber during the above-mentioned ignition operation. In a case in which the pressure in the combustion chamber at a time of ignition is not appropriate, even when the fuel-air mixture is combusted, sufficient energy is not acquired. Therefore, the engine cannot be appropriately started.
An object of the present invention is to provide an engine system and a straddled vehicle capable of appropriately starting an engine.

(1) An engine system according to one aspect of the present invention includes an engine unit that includes an engine and a rotation driver, a friction detector that detects a first parameter corresponding to friction of the engine, a pressure detector that detects a second parameter corresponding to pressure in a combustion chamber of the engine, and a controller that controls the engine unit based on the first parameter detected by the friction detector and the second parameter detected by the pressure detector, wherein the engine includes a fuel injection device arranged to inject fuel into an intake passage for leading air to the combustion chamber, an ignition device configured to ignite a fuel-air mixture in the combustion chamber, and a valve driver configured to respectively drive an intake valve that opens and closes an intake port and an exhaust valve that opens and closes an exhaust port, the rotation driver is configured to drive rotation of a crankshaft in forward and reverse directions, the controller controls the engine unit to perform a reverse rotation start-up operation during start-up of the engine, the fuel-air mixture is introduced into the combustion chamber while the crankshaft is rotated in the reverse direction, and the fuel-air mixture is ignited such that the crankshaft is rotated in the forward direction, in the reverse rotation start-up operation, and the controller sets an ignition threshold value based on the first parameter detected by the friction detector, and controls the ignition device such that the ignition is performed when the second parameter detected by the pressure detector reaches the set ignition threshold value, in the reverse rotation start-up operation.
In this engine system, during the start-up of the engine, the fuel-air mixture is introduced into the combustion chamber while the crankshaft is rotated in the reverse direction, and the introduced fuel-air mixture is ignited, whereby the fuel-air mixture is combusted. The crankshaft is driven in the forward direction by the energy generated by the combustion.
In this case, the ignition threshold value is set based on the first parameter corresponding to the friction of the engine. When the second parameter corresponding to the pressure in the combustion chamber of the engine reaches the ignition threshold value, the ignition of the fuel-air mixture by the ignition device is performed. Thus, when the pressure in the combustion chamber is an appropriate value corresponding to the friction of the engine, the fuel-air mixture in the combustion chamber can be ignited. Therefore, sufficient energy for driving the crankshaft in the forward direction can be acquired by the combustion of the fuel-air mixture. As a result, the engine can be appropriately started.
(2) The first parameter may be a value corresponding to a temperature of the engine. The higher the temperature of the engine is, the smaller the friction of the engine is, so that appropriate control corresponding to the friction of the engine can be performed based on the value corresponding to the temperature of the engine.
(3) The second parameter is a current flowing in the rotation driver. When the pressure in the combustion chamber is increased, the current flowing in the rotation driver is increased. Therefore, the fuel-air mixture in the combustion chamber can be ignited when the pressure in the combustion chamber is an appropriate value based on the current flowing in the rotation driver.
(4) The controller may adjust a torque generated by the rotation driver based on the first parameter detected by the friction detector in the reverse rotation start-up operation.
In this case, the crankshaft can be efficiently rotated in the reverse direction such that the second parameter reaches the ignition threshold value without excessive consumption of the electric power by the rotation driver.
(5) A straddled vehicle according to another aspect of the present invention includes a main body having a drive wheel, and an engine system, described above, that generates motive power for rotating the drive wheel.
In this straddled vehicle, the above-mentioned engine system is used, so that the engine can be appropriately started.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

Fig. 1 is a schematic side view showing a schematic configuration of a motorcycle according to one embodiment of the present invention;
Fig. 2 is a schematic diagram for explaining a configuration of an engine system;
Fig. 3 is a diagram for explaining a normal operation of the engine unit;
Fig. 4 is a diagram for explaining a reverse rotation start-up operation of the engine unit;
Figs. 5(a) to 5(c) are diagrams for explaining a case in which an engine is appropriately started in the reverse rotation start-up operation;
Figs. 6(a) to 6(c) are diagrams for explaining a case in which the engine is not appropriately started in the reverse rotation start-up operation;
Fig. 7 is a diagram showing one example of a threshold value setting map;
Figs. 8(a) to 8(c) are schematic diagrams for explaining setting of an ignition threshold value;
Fig. 9 is a diagram showing one example of a driving duty ratio setting map;
Figs. 10(a) to 10(c) are schematic diagrams for explaining setting of a target crank angle;
Fig. 11 is a flow chart of engine start-up processing; and
Fig. 12 is a flow chart of parameter setting processing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A motorcycle will be described below as one example of a straddled vehicle according to embodiments of the present invention with reference to drawings.

(1) Motorcycle

Fig. 1 is a schematic side view showing a schematic configuration of the motorcycle according to one embodiment of the present invention. In the motorcycle 100 of Fig. 1, a front fork 2 is provided at the front of a vehicle body 1 to be swingable in leftward and rightward directions. A handle 4 is attached to an upper end of the front fork 2, and a front wheel 3 is rotatably attached to a lower end of the front fork 2.
A seat 5 is provided at a substantially center of an upper portion of the vehicle body 1. An ECU (Engine Control Unit) 6 and an engine unit EU are provided below the seat 5. The engine unit EU includes a single-cylinder engine 10, for example. An engine system 200 is constituted by the ECU 6 and the engine unit EU. A rear wheel 7 is rotatably attached to a rear end of a lower portion of the vehicle body 1. The rotation of the rear wheel 7 is driven by motive power generated by the engine 10.

(2) Engine System

Fig. 2 is a schematic diagram for explaining a configuration of the engine system 200. As shown in Fig. 2, the engine unit EU includes the engine 10 and an integrated starter generator 14. The engine 10 includes a piston 11, a connecting rod 12, a crankshaft 13, an intake valve 15, an exhaust valve 16, a valve driver 17, an ignition plug 18 and an injector 19.
The piston 11 is provided to be reciprocatable in a cylinder 31 and connected to the crankshaft 13 via the connecting rod 12. The reciprocating motion of the piston 11 is transformed into the rotational motion of the crankshaft 13. The integrated starter generator 14 is provided at the crankshaft 13. The integrated starter generator 14 is a generator having a function of a starter motor, drives the rotation of the crankshaft 13 in forward and reverse directions and generates electric power by the rotation of the crankshaft 13. The forward direction is a rotation direction of the crankshaft 13 during a normal operation of the engine 10, and the reverse direction is the opposite direction. The integrated starter generator 14 directly transmits a torque to the crankshaft 13 without a reduction gear therebetween. The rotation of the crankshaft 13 in the forward direction (forward rotation) is transmitted to the rear wheel 7, so that the rotation of the rear wheel 7 is driven. The starter motor and the generator may be individually provided instead of the integrated starter generator 14.
A combustion chamber 31a is formed on the piston 11. The combustion chamber 31a communicates with an intake passage 22 through an intake port 21 and communicates with an exhaust passage 24 through an exhaust port 23. An intake valve 15 is provided to open and close the intake port 21, and an exhaust valve 16 is provided to open and close the exhaust port 23. The intake valve 15 and the exhaust valve 16 are driven by the valve driver 17. A throttle valve TV for adjusting a flow rate of air from the outside is provided at the intake passage 22. The ignition plug 18 is configured to ignite a fuel-air mixture in the combustion chamber 31a. The injector 19 is configured to inject fuel into the intake passage 22.
The ECU 6 includes a CPU (Central Processing Unit) and a memory, for example. A microcomputer may be used instead of the CPU and the memory. A main switch 40, a starter switch 41, an intake pressure sensor 42, a crank angle sensor 43, a current sensor 44 and a temperature sensor 45 are electrically connected to the ECU 6. The main switch 40 is provided below the handle 4 of Fig. 1, for example, and the starter switch 41 is provided at the handle 4 of Fig. 1, for example. The main switch 40 and the starter switch 41 are operated by a driver. The intake pressure sensor 42 detects pressure in the intake passage 22. The crank angle sensor 43 detects a rotation position of the crankshaft 13 (hereinafter referred to as a crank angle). The current sensor 44 detects an electric current flowing in the integrated starter generator 14 (hereinafter referred to as a motor current). The temperature sensor 45 detects a water temperature, an oil temperature or a machine temperature in the engine 10, for example, as a value corresponding to the temperature of the engine 10 (hereinafter referred to as an engine temperature).
The operations of the main switch 40 and the starter switch 41 are supplied to the ECU 6 as operation signals, and the detection results by the intake pressure sensor 42, the crank angle sensor 43, the current sensor 44 and the temperature sensor 45 are supplied to the ECU 6 as detection signals. The ECU 6 controls the integrated starter generator 14, the ignition plug 18 and the injector 19 based on the supplied operation signals and detection signals.

(3) Operation of Engine

For example, the engine 10 is started when the main switch 40 and the starter switch 41 of Fig. 2 are turned on, and the engine 10 is stopped when the main switch 40 of Fig. 2 is turned off. Further, the engine 10 may be automatically stopped when a predetermined idle stop condition is satisfied, and the engine 10 may be automatically restarted when a predetermined idle stop release condition is thereafter satisfied. The idle stop condition includes a condition that relates to at least one of a throttle opening (a degree of opening of the throttle valve TV), a vehicle speed and a rotation speed of the engine 10, for example. The idle stop release condition is that the throttle opening is larger than 0 when an accelerator grip is operated, for example. Hereinafter, a state in which the engine 10 is automatically stopped when the idle stop condition is satisfied is referred to as an idle stop state.
The engine unit EU performs a reverse rotation start-up operation during start-up of the engine 10. Thereafter, the engine unit EU performs the normal operation.
Fig. 3 is a diagram for explaining the normal operation of the engine unit EU. Fig. 4 is a diagram for explaining the reverse rotation start-up operation of the engine unit EU.
In the following description, a top dead center through which the piston 11 passes at the time of switching from a compression stroke to an expansion stroke is referred to as a compression top dead center, and a top dead center through which the piston 11 passes at the time of switching from an exhaust stroke to an intake stroke is referred to as an exhaust top dead center. A bottom dead center through which the piston 11 passes at the time of switching from the intake stroke to the compression stroke is referred to as an intake bottom dead center, and a bottom dead center through which the piston 11 passes at the time of switching from the expansion stroke to the exhaust stroke is referred to as an expansion bottom dead center.
In Figs. 3 and 4, a rotation angle in a range of two rotations (720 degrees) of the crankshaft 13 is indicated by one circle. The two rotations of the crankshaft 13 are equivalent to one cycle of the engine 10. The crank angle sensor 43 of Fig. 2 detects the rotation position in a range of one rotation (360 degrees) of the crankshaft 13. The ECU 6 determines which one of the two rotations of the crankshaft 13 equivalent to the one cycle of the engine 10 the rotation position detected by the crank angle sensor 43 corresponds to based on the pressure in the intake passage 22 detected by the intake pressure sensor 42. Thus, the ECU 6 can acquire the rotation position in the range of the two rotations (720 degrees) of the crankshaft 13.
In Figs. 3 and 4, an angle A0 is the crank angle when the piston 11 (Fig. 2) is positioned at the exhaust top dead center, an angle A2 is the crank angle when the piston 11 is positioned at the compression top dead center, an angle A1 is the crank angle when the piston 11 is positioned at the intake bottom dead center and an angle A3 is the crank angle when the piston 11 is positioned at the expansion bottom dead center. The arrow R1 indicates a direction in which the crank angle changes during the forward rotation of the crankshaft 13, and the arrow R2 indicates a direction in which the crank angle changes during the reverse rotation of the crankshaft 13. The arrows P1 to P4 indicate moving directions of the piston 11 during the forward rotation of the crankshaft 13, and the arrows P5 to P8 indicate the moving directions of the piston 11 during the reverse rotation of the crankshaft 13.

(3-1) Normal Operation

The normal operation of the engine unit EU will be described with reference to Fig. 3. During the normal operation, the crankshaft 13 (Fig. 2) is rotated in the forward direction. Thus, the crank angle changes in the direction of the arrow R1. In this case, as indicated by the arrows P1 to P4, the piston 11 (Fig. 2) falls in a range from the angle A0 to the angle A1, the piston 11 rises in a range from the angle A1 to the angle A2, the piston 11 falls in a range from the angle A2 to the angle A3 and the piston 11 rises in a range from the angle A3 to the angle A0.
At an angle A11, the fuel is injected into the intake passage 22 (Fig. 2) by the injector 19 (Fig. 2). In the forward direction, the angle A11 is positioned at a further advanced angle than the angle A0. Then, in a range from an angle A12 to an angle A13, the intake port 21 (Fig. 2) is opened by the intake valve 15 (Fig. 2). In the forward direction, the angle A12 is positioned at a further retarded angle than the angle A11 and a further advanced angle than the angle A0, and the angle A13 is positioned at a further retarded angle than the angle A1. The range from the angle A12 to the angle A13 is an example of a normal intake range. Thus, the fuel-air mixture including air and the fuel is introduced into the combustion chamber 31a (Fig. 2) through the intake port 21.
Next, at an angle A14, the fuel-air mixture in the combustion chamber 31a (Fig. 2) is ignited by the ignition plug 18 (Fig. 2). In the forward direction, the angle A14 is positioned at a further advanced angle than the angle A2. The fuel-air mixture is ignited, so that an explosion (combustion of the fuel-air mixture) occurs in the combustion chamber 31a. Energy of the combustion of the fuel-air mixture is turned into the driving force for the piston 11. Thereafter, in a range from an angle A15 to an angle A16, the exhaust port 23 (Fig. 2) is opened by the exhaust valve 16 (Fig. 2). In the forward direction, the angle A15 is positioned at a further advanced angle than the angle A3, and the angle A16 is positioned at a further retarded angle than the angle A0. The range from the angle A15 to the angle A16 is an example of a normal exhaust range. This causes the combusted gas to be exhausted from the combustion chamber 31a through the exhaust port 23.

(3-2) Reverse Rotation Start-up Operation

The reverse rotation start-up operation of the engine unit EU will be described with reference to Fig. 4. In the present example, the crank angle is adjusted in a predetermined reverse rotation starting range before the reverse rotation start-up operation is performed. The reverse rotation starting range is in a range from the angle A0 to the angle A2 in the forward direction, for example, and is preferably in a range from the angle A13 to the angle A2. In Fig. 4, the reverse rotation starting range is an angle A30. The angle A30 is in the range from the angle A13 to the angle A2.
In the reverse rotation start-up operation, the crankshaft 13 is rotated in the reverse rotation with the crank angle being in the reverse rotation starting range. Thus, the crank angle changes in the direction of the arrow R2. In this case, as indicated by the arrows P5 to P8, the piston 11 falls in a range from the angle A2 to the angle A1, the piston 11 rises in a range from the angle A1 to the angle A0, the piston 11 falls in a range from the angle A0 to the angle A3, and the piston 11 rises in a range from the angle A3 to the angle A2. The moving direction of the piston 11 during the reverse rotation of the crankshaft 13 is opposite to the moving direction of the piston 11 during the forward direction of the crankshaft 13.
In the present example, even during the reverse rotation of the crankshaft 13, the intake port 21 is opened in a range from the angle A13 to the angle A12, and the exhaust port 23 is opened in a range from the angle A16 to the angle A15, similarly to during the forward rotation of the crankshaft 13. However, during the reverse rotation of the crankshaft 13, the intake port 21 does not have to be opened in the range from the angle A13 to the angle A12, and further, the exhaust port 23 does not have to be opened in the range from the angle A16 to the angle A15.
At an angle A23, the fuel is injected into the intake passage 22 (Fig. 2) by the injector 19 (Fig. 2). In the reverse direction, the angle A23 is positioned at a further advanced angle than the angle A0. Further, in a range from an angle A21 to an angle A22, the intake port 21 (Fig. 2) is opened by the intake valve 15 (Fig. 2). The range from the angle A21 to the angle A22 is an example of a start-up intake range. In the reverse direction, the angles A21, A22 are in the range from the angle A0 to the angle A3. Because the piston 11 rises in a range from the angle A1 to the angle A0, even when the intake port 21 is opened in the range from the angle A13 to the angle A12, air and the fuel are hardly introduced into the combustion chamber 31a. On the other hand, because the piston 11 falls in the range from the angle A0 to the angle A3, the intake port 21 is opened in the range from the angle A21 to the angle A22, whereby a fuel-air mixture including air and the fuel is introduced into the combustion chamber 31a through the intake port 21 from the intake passage 22.
Subsequently, energization to an ignition coil connected to the ignition plug 18 (Fig. 2) is started at an angle A31a, and the fuel-air mixture in the combustion chamber 31a is ignited by the ignition plug 18 (Fig. 2) at an angle A31. In the reverse direction, the angle A31a is positioned at a further advanced angle than the angle A31, and the angle A31 is positioned at a further advanced angle than the angle A2. The angle A31 is an example of a start-up ignition range. In the present embodiment, when the motor current detected by the current sensor 44 of Fig. 2 reaches a threshold value, the fuel-air mixture is ignited by the ignition plug 18. Details of ignition control will be described below.
Further, at the angle A31, the rotation direction of the crankshaft 13 is switched from the reverse direction to the forward direction. In this case, a torque of the crankshaft 13 in the forward direction is increased by the combustion of the fuel-air mixture. Thereafter, the engine 10 is shifted to the normal operation of Fig. 3.
In the present embodiment, the fuel-air mixture in the combustion chamber 31a is ignited by the ignition plug 18 simultaneously with the stop of the reverse rotation of the crankshaft 13. However, if the crankshaft 13 can be driven in the forward direction, the stop of the reverse rotation of the crankshaft 13 and the ignition by the ignition plug 18 do not have to be performed simultaneously.
In this manner, in the present embodiment, the fuel-air mixture is led to the combustion chamber 31a while the crankshaft 13 is rotated in the reverse rotation by the integrated starter generator 14, and with the piston 11 being close to the compression top dead center, the fuel-air mixture in the combustion chamber 31a is thereafter ignited, during the start-up of the engine 10. Thus, the piston 11 is driven such that the crankshaft 13 is rotated in the forward direction.

(4) Friction of Engine

The friction of the engine 10 fluctuates depending on the state of the engine 10. For example, the lower the engine temperature is, the larger the friction of the engine 10 is. As described above, in the reverse rotation start-up operation, when the motor current reaches a threshold value (hereinafter referred to as an ignition threshold value), the fuel-air mixture in the combustion chamber 31a is ignited. In a case in which the ignition threshold value is constant, the engine 10 is not appropriately started sometimes in the above-mentioned reverse rotation start-up operation due to the fluctuation of the friction of the engine 10.
The reverse rotation start-up operation in a case in which the ignition threshold value is constant will be described. Figs. 5(a) to 5(c) are diagrams for explaining a case in which the engine 10 is appropriately started in the reverse rotation start-up operation. Figs. 6(a) to 6(c) are diagrams for explaining a case in which the engine 10 is not appropriately started in the reverse rotation start-up operation.
In the example of Figs. 5(a) to 5(c), the reverse rotation start-up operation is performed with the engine temperature being relatively high during re-start of the engine 10 from the idle stop state, for example. In this case, the friction of the engine 10 is relatively small. On the other hand, in the example of Figs. 6(a) to 6(c), the reverse rotation start-up operation is performed with the engine temperature being relatively low during cold start-up, for example. In this case, the friction of the engine 10 is relatively large.
In Figs. 5(a) and 6(a), the abscissa indicates the crank angle, and the ordinate indicates a rotational load of the crankshaft 13. In Figs. 5(b) and 6(b), the abscissa indicates the crank angle, and the ordinate indicates the motor current. In Figs. 5(c) and 6(c), the abscissa indicates the crank angle, and the ordinate indicates the pressure in the combustion chamber 31a (hereinafter referred to as cylinder inner pressure).
In the example of Fig. 5(a), the rotational load of the crankshaft 13 changes in a range of not less than a value V1 and not more than a value V2. When the crank angle is at the angle A2 corresponding to the compression top dead center, the rotational load of the crankshaft 13 becomes the maximum value V2. Further, between the angle A1 and the angle A0, the rotational load of the crankshaft 13 is increased in order to drive the intake valve 15. Further, between the angle A0 and the angle A3, the rotational load of the crankshaft 13 is increased in order to drive the exhaust valve 16.
As shown in Fig. 5(b), in the reverse rotation start-up operation, with the crank angle being at the angle A30, the motor current becomes a positive value. Thus, the crankshaft 13 is driven in the reverse direction by the integrated starter generator 14. At a time of the start of the reverse rotation of the crankshaft 13, the motor current is decreased after the motor current is temporarily increased. Thereafter, with an increase in rotational load of the crankshaft 13, a load exerted on the integrated starter generator 14 is increased, so that the motor current is increased. Specifically, between the angle A1 and the angle A0 and between the angle A0 and the angle A3, the motor current is increased. Further, when the crank angle is close to the angle A2 corresponding to the compression top dead center, the motor current is increased. When the motor current reaches a constant ignition threshold value Vt, the fuel-air mixture in the combustion chamber 31a (Fig. 2) is ignited, and the crankshaft 13 is driven in the forward direction by the integrated starter generator 14. In the present example, when the motor current reaches the ignition threshold value Vt, the crank angle is the angle A31.
As shown in Fig. 5(c), when the crank angle reaches the angle A31, the cylinder inner pressure becomes a value Ps. In this state, the fuel-air mixture is ignited, so that the fuel-air mixture is combusted. In the present example, sufficient energy is acquired by the combustion of the fuel-air mixture. Thus, as shown in Fig. 5(a), the crankshaft 13 can exceed the angle A2 corresponding to a first compression top dead center.
In the example of Figs. 6(a) to 6(c), differences from the example of Figs. 5(a) to 5(c) will be described. In the example of Figs. 6(a) to 6(c), the friction of the engine 10 is larger than the example of Figs. 5(a) to 5(c). Therefore, as shown in Fig. 6(a), the rotational load of the crankshaft 13 changes in a range of not less than a value V3 and not more than a value V4. The value V3 is larger than the value V1, and the value V4 is larger than the value V2.
Thus, in the entire range of the crank angle, a load exerted on the integrated starter generator 14 (Fig. 2) is increased. Therefore, as shown in Fig. 6(b), in the entire range of the crank angle, the motor current is larger than the example of Fig. 5(b).
When the motor current reaches the constant ignition threshold value Vt, the fuel-air mixture in the combustion chamber 31a (Fig. 2) is ignited, and the crankshaft 13 is driven in the forward direction by the integrated starter generator 14. In the present example, when the motor current reaches the ignition threshold value Vt, the crank angle is an angle A31s. The angle A31s is positioned at a further advance angle than the angle A31 in the reverse direction.
The cylinder inner pressure depends on the crank angle. As shown in Fig. 6(c), when the crank angle reaches the angle A31s, the cylinder inner pressure becomes a value Psa. The value Psa is smaller than the value Ps. In this state, the fuel-air mixture in the combustion chamber 31a is ignited, so that the fuel-air mixture is combusted. The lower the cylinder inner pressure of when the fuel-air mixture is ignited is, the smaller the energy acquired by the combustion of the fuel-air mixture is. In the present example, sufficient energy is not acquired by the combustion of the fuel-air mixture. Therefore, as shown in Fig. 6(a), the crankshaft 13 cannot exceed the angle A2 corresponding to the first compression top dead center.
In this manner, in a case in which the friction of the engine 10 is different each time, a relationship between the motor current and the cylinder inner pressure is different each time. Therefore, when the ignition threshold value is constant, variations are generated in the cylinder inner pressure of when the fuel-air mixture is ignited due to the fluctuation of the friction of the engine 10.
As in the example of Figs. 6(a) to 6(c), when the fuel-air mixture in the combustion chamber 31a is ignited with the cylinder inner pressure not being sufficiently high, sufficient energy for rotating the crankshaft 13 in the forward direction is not acquired. Thus, the engine 10 cannot be appropriately started.

(5) Setting of Ignition Threshold Value

It is necessary to adjust the cylinder inner pressure of when the fuel-air mixture is ignited with high accuracy in order to acquire sufficient energy by the combustion of the fuel-air mixture. Therefore, in the present embodiment, the ignition threshold value is suitably set in order to correspond to the friction of the engine 10.
For example, a map indicating a relationship between the engine temperature and the ignition threshold value (hereinafter referred to as a threshold value setting map) is stored in the memory of the ECU 6 of Fig. 2. The threshold value setting map is acquired by an experiment, simulation or the like. Fig. 7 is a diagram indicating one example of the threshold value setting map. In Fig. 7, the abscissa indicates the engine temperature, and the ordinate indicates the ignition threshold value.
As shown in Fig. 7, in the threshold value setting map, the relationship between the engine temperature and the ignition threshold value is determined such that the higher the engine temperature is, the smaller the ignition threshold value is. The ECU 6 sets the ignition threshold value corresponding to the engine temperature based on the threshold value setting map. As described above, there is a correlation between the engine temperature and the friction of the engine 10. Therefore, the larger the friction of the engine 10 is, the larger the set ignition threshold value is. In this case, even in a case in which the friction of the engine 10 is different each time, the ignition threshold value is adjusted such that the crank angle of when the fuel-air mixture is ignited is constant. Hereinafter, a target value of the crank angle at which the fuel-air mixture is to be ignited is referred to as a target angle. In the present example, the target angle is the angle A31.
Figs. 8(a) to 8(c) are schematic diagrams for explaining the setting of the ignition threshold value. Similarly to Figs. 5(a) to 5(c) and Figs. 6(a) to 6(c), in Figs. 8(a) to 8(c), the abscissa indicates the crank angle, and the ordinate respectively indicates the rotational load, the motor current and the cylinder inner pressure.
In the example of Figs. 8(a) to 8(c), the friction of the engine 10 is the same as the example of Figs. 6(a) to 6(c). Therefore, as shown in Fig. 8(a), the rotational load of the crankshaft 13 changes in the range of not less than the value V3 and not more than the value V4. The example of Figs. 8(a) to 8(c) is different from the example of Figs. 6(a) to 6(c) in the following points.
As shown in Fig. 8(b), the ignition threshold value is set to a value Vta. The value Vta is higher than the value Vt. In this case, when the motor current reaches the ignition threshold value Vta, the crank angle is the angle A31. When the motor current reaches the ignition threshold value Vta, the fuel-air mixture in the combustion chamber 31a is ignited, and the crankshaft 13 is driven in the forward direction by the integrated starter generator 14.
As shown in Fig. 8(c), when the crank angle reaches the angle A31, the cylinder inner pressure becomes the value Ps. In this state, the fuel-air mixture in the combustion chamber 31a is ignited, so that the fuel-air mixture is combusted. Thus, sufficient energy is acquired by the combustion of the fuel-air mixture similarly to the example of Figs. 5(a) to 5(c). Therefore, as shown in Fig. 8(a), the crank angle can exceed the angle A2 corresponding to the first compression top dead center.

(6) Driving Duty Ratio (Driving Duty Cycle)

A torque generated by the integrated starter generator 14 depends on a duty ratio of the current supplied to the integrated starter generator 14 (hereinafter referred to as a driving duty ratio). In the reverse rotation start-up operation, when the driving duty ratio is low, the crank angle may not be able to reach the target angle. In particular, as in the example of Figs. 6(a) to 6(c), when the friction of the engine 10 is large, the reverse rotation of the crankshaft 13 may be stopped due to the rotational load of the crankshaft 13 before the crank angle reaches the target angle.
On the other hand, when the driving duty ratio is high, the crank angle easily reaches the target angle. However, electric power may be excessively consumed. In particular, as in the example of Figs. 5(a) to 5(c), in a case in which the friction of the engine 10 is small, even when the torque generated by the integrated starter generator 14 is small, the crank angle can reach the target angle. Therefore, when the driving duty ratio is high, the electric power is excessively consumed.
The driving duty ratio may be adjusted to correspond to the friction of the engine 10. For example, a map indicating a relationship between the engine temperature and the driving duty ratio (hereinafter referred to as a driving duty ratio setting map) is stored in the memory of the ECU 6 of Fig. 2. The driving duty ratio setting map is acquired by an experiment, simulation or the like. Fig. 9 is a diagram showing one example of the driving duty ratio setting map. In Fig. 9, the abscissa indicates the engine temperature, and the ordinate indicates the driving duty ratio.
As shown in Fig. 9, in the driving duty ratio setting map, the relationship between the engine temperature and the driving duty ratio is determined such that the higher the engine temperature is, the lower the driving duty ratio is. The ECU 6 sets the driving duty ratio corresponding to the engine temperature based on the driving duty ratio map. In this case, the larger the friction of the engine 10 is, the higher the set driving duty ratio is.
In this manner, the driving duty ratio is adjusted to correspond to the friction of the engine 10, whereby the crank angle can be adjusted to the target angle while the electric power is prevented from being excessively consumed.

(7) Adjustment of Target Angle

In a case in which the friction of the engine 10 is different each time, a necessary torque of the crankshaft 13 in the forward direction for the crank angle to exceed the angle A2 corresponding to the first compression top dead center is different each time. The smaller the friction of the engine 10 is, the smaller the necessary torque of the crankshaft 13 in the forward direction is.
As described above, the torque of the crankshaft 13 in the forward direction acquired by the reverse rotation start-up operation depends on the cylinder inner pressure of when the fuel-air mixture is ignited, and the cylinder inner pressure depends on the crank angle. Therefore, the target angle may be adjusted to correspond to the friction of the engine 10.
It is possible to adjust the crank angle of when the fuel-air mixture is ignited by adjusting the ignition threshold value. In the threshold value setting map of Fig. 7, even in a case in which the friction of the engine 10 is different each time, the relationship between the engine temperature and the ignition threshold value is determined such that the target angle is constant. Alternatively, the relationship between the engine temperature and the ignition threshold value may be set such that the smaller the friction of the engine 10 is, the farther the target angle is from the angle A2.
Figs. 10(a) to 10(c) are schematic diagrams for explaining the adjustment of the target angle. Similarly to Figs. 5(a) to 5(c) and Figs. 6(a) to 6(c), in Figs. 10(a) to 10(c), the abscissa indicates the crank angle, and the ordinate respectively indicates the rotational load, the motor current and the cylinder inner pressure.
In the example of Figs. 10(a) to 10(c), differences from the example of Figs. 5(a) to 5(c) will be described. In the example of Figs. 10(a) to 10(c), the friction of the engine 10 is smaller than the example of Figs. 5(a) to 5(c). Therefore, as shown in Fig. 10(a), the rotational load of the crankshaft 13 changes in a range of not less than a value V5 and not more than a value V6. The value V5 is smaller than the value V1, and the value V6 is smaller than the value V2.
Further, in Fig. 10(b), in the entire range of the crank angle, the motor current is smaller than the example of Fig. 5(b). The ignition threshold value is set to a value Vtb. The value Vtb is lower than the value Vt. In this case, when the motor current reaches the ignition threshold value Vtb, the crank angle is an angle A31t. In the present example, the angle A31t is the target angle and is positioned at a further advanced angle than the angle A31 in the reverse direction. When the motor current reaches the ignition threshold value Vtb, the fuel-air mixture in the combustion chamber 31a is ignited, and the crankshaft 13 is driven in the forward direction by the integrated starter generator 14.
As shown in Fig. 10(c), when the crank angle reaches the angle A31t, the cylinder inner pressure becomes a value Psb. The value Psb is smaller than the value Ps. In this state, the fuel-air mixture in the combustion chamber 31a is ignited, so that the fuel-air mixture is combusted. In this case, because the friction of the engine 10 is small, even when the energy acquired by the combustion of the fuel-air mixture is smaller than the example of Figs. 5(a) to 5(c), the crankshaft 13 can exceed the angle A2 corresponding to the first compression top dead center.
In this manner, the target angle is adjusted to correspond to the friction of the engine 10, so that the necessary torque of the crankshaft 13 in the forward direction can be acquired while the electric power consumed by the integrated starter generator 14 is reduced in the reverse rotation start-up operation.
The ignition control may be performed based on the crank angle instead of the motor current. Specifically, when the crank angle acquired from the detection results of the intake pressure sensor 42 (Fig. 2) and the crank angle sensor 43 (Fig. 2) reaches the target angle, the fuel-air mixture in the combustion chamber 31a may be ignited.
Further, the ignition control based on the motor current and the ignition control based on the crank angle may be combined. For example, the ignition threshold value and the target angle may be respectively set to correspond to the friction of the engine 10, and the fuel-air mixture in the combustion chamber 31a may be ignited at a point of time at which any one of a condition in which the motor current detected by the current sensor 44 reaches the ignition threshold value and a condition in which the crank angle detected by the intake pressure sensor 42 and the crank angle sensor 43 reaches the target angle is satisfied.

(8) Engine Start-up Processing

The ECU 6 performs the engine start-up processing based on the control program stored in the memory in advance. Fig. 11 is a flow chart of the engine start-up processing. The engine start-up processing is performed when the main switch 40 of Fig. 2 is turned on or when the engine 10 is switched to the idle stop state, for example.
As shown in Fig. 11, the ECU 6 determines whether a predetermined start-up condition is satisfied (step S1). When the engine unit EU is not in the idle stop state, the start-up condition is that the starter switch 41 (Fig. 2) is turned on, for example. When the engine unit EU is in the idle stop state, the start-up condition is that the idle stop release condition is satisfied.
When the start-up condition is not satisfied, the ECU 6 repeats the processing of step S1 until the start-up condition is satisfied. When the start-up condition is satisfied, the ECU 6 performs parameter setting processing (step S2). The ignition threshold value and the driving duty ratio are set by the parameter setting processing. Details of the parameter setting processing will be described below. Subsequently, the ECU 6 controls the integrated starter generator 14 such that the crankshaft 13 is rotated in the reverse direction (step S3). In this case, the integrated starter generator 14 is controlled using the driving duty ratio set by the parameter setting processing.
At a time of the start of the engine start-up processing, when the crank angle is not in the reverse rotation starting range (the angle A30), the crank angle may be adjusted in the reverse rotation starting range before the crankshaft 13 is rotated in the reverse direction as described above.
Next, the ECU 6 determines whether a fuel injection condition is satisfied (step S4). For example, the fuel injection condition is that the crank angle acquired from the detection results of the intake pressure sensor 42 (Fig. 2) and the crank angle sensor 43 (Fig. 2) reaches the angle A23 of Fig. 4. When the fuel injection condition is not satisfied, the ECU 6 repeats the processing of step S3. When the fuel injection condition is satisfied, the ECU 6 controls the injector 19 (Fig. 2) such that the fuel is injected into the intake passage 22 (Fig. 2) (step S5). In this case, the ECU 6 may control the injector 19 in response to a pulse signal from the crank angle sensor 43.
Then, the ECU 6 determines whether an energization starting condition is satisfied (step S6). For example, the energization starting condition is that the crank angle acquired from the detection results of the intake pressure sensor 42 (Fig. 2) and the crank angle sensor 43 (Fig. 2) reaches the angle A31a of Fig. 4. When the energization starting condition is not satisfied, the ECU 6 repeats the processing of step S6. When the energization starting condition is satisfied, the ECU 6 starts the energization to the ignition coil (step S7). In this case, the ECU 6 may control the ignition coil in response to the pulse signal from the crank angle sensor 43.
Next, the ECU 6 determines whether an ignition condition is satisfied (step S8). In the present example, the ignition condition is that the motor current detected by the current sensor 44 (Fig. 2) reaches the ignition threshold value set in the parameter setting processing of step S2.
When the ignition condition is not satisfied, the ECU 6 repeats the processing of step S8. When the ignition condition is satisfied, the ECU 6 controls the integrated starter generator 14 such that the crankshaft 13 is rotated in the forward direction (step S9), and controls the ignition plug 18 such that the fuel-air mixture in the combustion chamber 31a is ignited (step S10). Thus, the engine start-up processing is finished.
The parameter setting processing of step S2 will be described. Fig. 12 is a flow chart of the parameter setting processing. As shown in Fig. 12, the ECU 6 acquires the engine temperature detected by the temperature sensor 45 (step S11).
Next, the ECU 6 sets the ignition threshold value based on the acquired engine temperature (step S12). For example, the ignition threshold value corresponding to the acquired engine temperature is acquired from the threshold value setting map of Fig. 7, for example. In this case, as in the example of Figs. 8(a) to 8(c), the ignition threshold value may be set such that the target angle is constant, or as in the example of Figs. 10(a) to 10(c), the ignition threshold value may be set such that the target angle is different each time.
Then, the ECU 6 sets the driving duty ratio based on the acquired engine temperature (step S13). For example, the driving duty ratio corresponding to the acquired engine temperature is acquired from the driving duty ratio setting map of Fig. 9. In this manner, the ignition threshold value and the driving duty ratio are set, so that the parameter setting processing is finished.

(9) Effects

In the engine system 200 according to the present embodiment, during the start-up of the engine 10, the fuel-air mixture is introduced into the combustion chamber 31a while the crankshaft 13 is rotated in the reverse direction, and the fuel-air mixture in the combustion chamber 31a is ignited when the motor current reaches the ignition threshold value. In this case, because the ignition threshold value is set based on the engine temperature corresponding to the friction of the engine 10, the fuel-air mixture in the combustion chamber 31a is ignited when the cylinder inner pressure is an appropriate value corresponding to the friction of the engine 10. Therefore, sufficient energy for driving the crankshaft 13 in the forward direction is acquired by the combustion of the fuel-air mixture. As a result, the engine 10 can be appropriately started.
Further, because ignition control is performed using the engine temperature detected by the temperature sensor 45 and the motor current detected by the current sensor 44, appropriate control corresponding to the friction of the engine 10 can be performed while the configuration is inhibited from being complicated.

(10) Other Embodiments

While the engine temperature is used as a parameter corresponding to the friction of the engine 10 in the above-mentioned embodiment, the present invention is not limited to this. Another parameter corresponding to the friction of the engine 10 may be used. For example, the rotational load of the crankshaft 13 is detected, and the detected value may be used as the parameter corresponding to the friction of the engine 10.
While the above-mentioned embodiment is an example in which the present invention is applied to the motorcycle, the invention is not limited to such. The present invention may be applied to another straddled vehicle or saddle-straddling type motor vehicle such as a motor tricycle, an All-Terrain Vehicle (ATV) or the like.

(11) Correspondences between Constituent Elements in Claims and Parts in Preferred Embodiments

In the following paragraphs, non-limiting examples of correspondences between various elements recited in the claims below and those described above with respect to various preferred embodiments of the present invention are explained.
In the above-mentioned embodiment, the engine system 200 is an example of an engine system, the engine unit EU is an example of an engine unit, the engine 10 is an example of an engine, an integrated starter generator 14 is an example of a rotation driver, the temperature sensor 45 is an example of a friction detector, the current sensor 44 is an example of a pressure detector, the ECU 6 is an example of a controller, the injector 19 is an example of a fuel injection device, the ignition plug 18 is an example of an ignition device and the valve driver 17 is an example of a valve driver. Further, the motorcycle 100 is an example of a straddled vehicle, the vehicle body 1 is an example of a main body and the rear wheel 7 is an example of a drive wheel.
As each of various elements recited in the claims, various other elements having configurations or functions described in the claims can be also used.

INDUSTRIAL APPLICABILITY

The present invention can be effectively utilized for various types of engine systems and straddled vehicles.

Claims

An engine system (200) comprising:
an engine unit (EU) that includes an engine (10) and a rotation driver (14);

a friction detector (45) configured to detect a first parameter corresponding to friction of the engine (10);

a pressure detector (44) configured to detect a current flowing in the rotation driver (14) as a second parameter corresponding to pressure in a combustion chamber (31a) of the engine (10); and

a controller (ECU) configured to control the engine unit (EU) based on the first parameter detected by the friction detector (45) and the second parameter detected by the pressure detector (44), wherein

the engine (10) includes

a fuel injection device (19) arranged to inject fuel into an intake passage (22) for leading air to the combustion chamber (31a),

an ignition device (18) configured to ignite a fuel-air mixture in the combustion chamber (31a), and

a valve driver (17) configured to respectively drive an intake valve (15) configured to open and close an intake port (21) and an exhaust valve (16) configured to open and close an exhaust port (23),

the rotation driver (14) is configured to drive rotation of a crankshaft (13) in forward and reverse directions,

the controller (ECU) is configured to control the engine unit (EU) to perform a reverse rotation start-up operation during start-up of the engine (10),

wherein the fuel-air mixture is introduced into the combustion chamber (31a) while the crankshaft (13) is rotated in the reverse direction, and the fuel-air mixture is ignited such that the crankshaft (13) is rotated in the forward direction, in the reverse rotation start-up operation,

wherein the controller (ECU) is configured to set an ignition threshold value based on the first parameter detected by the friction detector (45) such that the larger the friction of the engine (10) is, the larger the ignition threshold value is, and to control the ignition device (18) such that the ignition is performed when the current detected by the pressure detector (44) reaches the set ignition threshold value, in the reverse rotation start-up operation, and

a relationship between the first parameter and the ignition threshold value is determined such that a crank angle of when the fuel-air mixture is ignited is constant.
The engine system (200) according to claim 1, wherein
the first parameter is a value corresponding to a temperature of the engine (10).
The engine system (200) according to claim 1 or 2, wherein
the controller (ECU) is configured to adjust a torque generated by the rotation driver (14) based on the first parameter detected by the friction detector (45) in the reverse rotation start-up operation.
A straddled vehicle (100), comprising:
a main body (1) having a drive wheel (7); and

an engine system (200) according to any one of claims 1 to 3 that is configured to generate motive power for rotating the drive wheel (7).